


We Without Wings

by somnivagrantTraviatus



Series: Undergods [1]
Category: Undertale (Video Game)
Genre: Gen, also assorted other monsters, discworld-inspired Death, gratuitous formatting, reapertale
Language: English
Status: Completed
Published: 2015-12-18
Updated: 2016-01-26
Packaged: 2018-05-07 09:39:15
Rating: Teen And Up Audiences
Warnings: No Archive Warnings Apply
Chapters: 10
Words: 13,463
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/5452025
Author URL: https://archiveofourown.org/users/somnivagrantTraviatus/pseuds/somnivagrantTraviatus
Summary: <blockquote class="userstuff">
              <p>Sans falls, then forgets. Gaster might be the key to why he's here, but that doesn't mean they're working toward all the same goals.</p><p>Inspired by and based off of Renrink's Reapertale AU.</p>
            </blockquote>





	1. The Fall

**Summary for the Chapter:**

> Why Sans drinks ketchup. Also, there are puns.

He had been cruel, once.

He hadn't meant to be. Back then, he hadn't meant to be much of anything. He had a job to do, that was all, and he did it dispassionately and even-handedly. When the lifetimers ran out, he would find the monsters whose time was up, and slice the threads that tied their soul to their bodies. That done, the monsters would turn to dust, and that was that. 

But something big was looming, something wrong. Monsters and humans alike could die, because they were alive at some point, but how could something without life die? And yet, it would happen. Time would, at some point, die. Everything would stop. He could feel it in his bones.

**_HAH HAH._**

Never let it be said that Death was without a sense of humor.

Still, this was an anomaly, and a frustrating one at that. It could not be allowed to happen. He took his job very seriously, and that included preventing any deaths that weren't supposed to happen, even (or especially?) that of time itself. But how to proceed? He had learned as much as he could by himself, so, logically, that meant he now required assistance. Life would be even more useless in this matter than he was - she dealt with the messy, chaotic now, not the clean lines of the future. That left only the monsters he guided. He would have to find a monster skilled enough to work out what was happening, smart enough to figure out how to stop it, yet strong enough not to fall prey to the tendencies that came with physical forms. Tendencies like not wanting to work alongside the physical manifestation of death, for example, or being afraid of what it would mean for one’s entire race to be slaughtered by a malevolent demon before said demon consumed time itself.

Still, even incorporated into a physical form, instead of the pure determination to fulfill his duty that was his standard self, wandering the physical plane tended to arouse more suspicion than would be prudent. He would have to bleed off the excess power and leave it behind when he incorporated. Hopefully, that would make him less noticeable to prying eyes.

So he tore away part of his power, leaving only a thin trickle by which to find it again, and with it went his capital letters, his wings, and all but the most necessary of his memories. _now i am without_ , he thought to himself, and, with the kind of grin only a skull could grin, Sans allowed himself to fall, down and away from Death, until at last he awoke, with no memory of who he was or how he had gotten there.

Sans went over what he knew. _my name is sans_ , he thought to himself. _i’m a skeleton. something very bad is coming, and i need to figure out what it is and how to stop it._ He paused. _also, i need to eat something._

( ** _I’VE NEVER EATEN BEFORE_** , said the part of him that was still Death. **_I WONDER WHAT IT’S LIKE?_** )

Brushing off the errant thought with ingrained ease (Of course he'd eaten before! He just… couldn't recall when), Sans pushed his hood down around his neck and took a look around. He was leaning against a tree, having obviously just woken up from a nap. In front of him was a large, sheer cliff. To the northwest, there were the glinting lights of what appeared to be a small, snowbound town. perfect. A place like that had to have a bar of some sort, where the residents could warm themselves with food and company. If he was really lucky, Sans could ask around about anyone who might know something about disturbances in the timeline.

The town looked far away, but that was no problem. Easily spying a small tear in the fabric of reality, Sans slipped through it, knowing instinctively that the glowing lines of characters floating in this not-space couldn't harm him. A blink of an eye later, and Sans could see the cliff he had just been standing on and how it loomed large over the nearby forest. “good thing i didn't have to walk this far,” he remarked. 

The town was cheery, if chilly, with log cabin houses scattered along the main street and little flowers poking up here and there through the snow. And - yes, there was the little bar, just as he had guessed. Grillby’s, it was called, and Sans’s natural smile grew as he pushed the door open and walked in.

The bar was sparsely populated, though Sans guessed that in a small town like this, it would be considered a fairly large crowd. A couple of monsters sat at the booths, a group of dogs were gathered around the tables (was that one playing poker against itself somehow?), and a few more monsters were scattered at the front, between the jukebox and the bar itself. Behind the counter stood a tall, flickering flame in a suit. _at a guess_ , Sans thought, _i’d say that’s grillby._

Every head in the place had turned towards the door when he walked in (though Grillby’s gaze had returned to the glass he was cleaning almost immediately afterwards), so Sans tossed a few nods and waves at the crowd as he made his way up to the bar. There was no menu posted, probably because the residents of a town this small would have the menu memorized already, so he’d have to improvise. “...i’ll have a bottle of your finest,” he said, and then hazarded, “and a burger.”

Grillby nodded, then crackled something. “He asked if you wanted fries with that,” one of the patrons helpfully translated.

“sure, fries sound fine,” Sans answered, and settled down to wait.

A few minutes later, there was a clink as a plate and a bottle were set in front of him. Grillby stepped back after setting down his order and resumed polishing the glasses, but it was obvious that he was waiting for Sans’s reaction.

The plate looked normal enough. The burger (a veggie burger, naturally, what with the shortages of meat underground) was a little more well done than he thought he might like, but he hadn't really planned on eating it, anyway. The bottle was unmarked, made of either glass or clear, hard plastic, and filled with an opaque, red liquid. As he held the bottle up and inspected it, unclear ( _heh_ ) as to what kind of a drink it was, the crowd’s eyes once again swiveled to him.

He uncapped the bottle. The bar held its breath.

Slowly, he tipped it back, letting the liquid (substance? It was a little thick to really be called a liquid) flow down his nonexistent throat.

When he had drained the bottle, he set it back on the counter, perpetual grin still on his face. “nice. i think i like that stuff. what is it?”

The tension in the room broke like it had never been there to begin with. “It’s ketchup,” cried one of the patrons, an unsteady looking bunny. “And you - you actually drank it?”

Sans looked down at the empty bottle, as if in surprise, then shrugged. “sure looks that way. don't worry, though. i really relished it.”

There was a pause as the crowd tried to figure out whether or not he had actually just said that, but it was quickly broken with his wink, as the crowd simultaneously came to the conclusion that, yes, he had actually just said that. Groans rebounded off the walls, and, just like that, he was one of them. The other patrons clambered over themselves to sit next to him, talking over each other as they asked about who he was, where he was from, and what he was doing there. Sans answered what he could and made up plausible excuses for the rest, and, finally, asked where he could find someone who might know a thing or two about quantum physics.

“I have no idea what that means,” said one of the dogs. “Which means that you should probably ask the Royal Scientist.”

“Yeah, the Royal Scientist should be able to help you,” a few other patrons echoed. Sans stood up, clearing a bit of space around his bar stool.

“sounds like i need to find the royal scientist then. any idea where they might be?”

The other monsters conferred with each other, then appeared to come to an agreement. “Gaster’s lab is in Hotland,” said the bunny from earlier. “He doesn't get out much, so he'll probably be there, but he's working on an extremely important project for the k-k-king! So he might not have time for you.”

“i guess i’ll see about that when i get there.” Hands in his pockets, Sans walked away from the counter, the crowd parting around him like the Red Sea. At the door, he turned, addressing the crowd once more. “thanks for the evening, folks. i had a good time. see you around, maybe.” That said, he walked out the door and was gone.

(“He didn't even touch his food,” the plant-like monster with the big mouth remarked after the skeleton had gone. “It'd be a shame to throw it out, so I'll finish it off for him. I was getting kind of peckish anyway.” So saying, they sat down, causing a PPPBBBBTTTTHHFFFTHD noise to fill the room as the whoopie cushion Sans had left on his stool was deflated. After the initial shocked silence and uproarious laughter, they found a note under the whoopie cushion, along with a few gold coins. The note said:

_“sorry. i know this isn't enough for the food, but i’m a little low on gold. don’t worry, i’ll make sure to come back and pay the rest of the bill as soon as i can spare the cash. in the meantime, put the rest on my tab. hopefully the laughs from tonight will tide me over til then. -sans”_

The room was silent. Then, one by one, the monsters came up to the bar and left some gold by the now-empty plate and grease-stained note, until the bill had been fully paid and then some. “Put the extra on his tab, Grillbz,” one monster suggested. “He looked like he could use the extra cash, and besides, I haven't laughed so hard in a long time.”

Grillby nodded, the light reflecting off his glasses. He crackled something.

The patrons all nodded. “Yeah. I hope he comes back, too.”)


	2. The Royal Scientist

**Summary for the Chapter:**

> Sans visits Gaster's lab and scores himself a position as the scientist's coworker. He'd feel better about that if he had any idea how he did it.

Sans reappeared at the border between Waterfall and Hotland, mopping his brow more for the sentiment of the gesture than for any relief it might provide. As he might have guessed from the name, Hotland was sweltering, and Sans was glad to be unaffected by heat so that he could keep his hoodie on. Now that he was here, the next orders of business would be to find the Royal Scientist, and somehow convince him both that there was a problem, and that he and Sans needed to work together to fix it. Sans heaved a sigh. Really, it seemed so much simpler to just forget about the whole thing and go home (did he even have a home? He couldn't remember).

But something inside him wouldn't let him leave the problem be. **_THIS IS IMPORTANT_** , it said, in the kind of voice that was impossible to ignore. **_YOU MUST KEEP GOING. IT IS YOUR ONLY PURPOSE._**

Sans wasn't sure if that was comforting or terrifying. Or maybe both.

He stopped a passing Vulkin to ask for directions, then ignored those directions and took a shortcut to where he estimated the lab should roughly be based on them instead. When he arrived on a barren expanse of cratered lavarock, he was confused for only a few seconds before logic caught up to him. After quickly double-checking his math (perfect, as always, though it could never hurt to be too sure), he felt along the ground with the same sense he used to locate his shortcuts. As he had suspected, there were multiple rooms under the ground there. _pretty strange place for a lab, if you ask me,_ he thought with a shrug, as he found a shortcut that would take him to the labs and stepped through it. _then again… he’s supposed to have some big secret project going on for the king, right? they're probably down there for easier access to something they need for that. geothermal power, maybe. that'd make sense. it's not like they can run the underground off magic forever._

The room he arrived in had only one other occupant: a tall, thin, stick of a monster with hands that looked like they should be trembling. They weren't, though Sans got the sense that it wouldn't take much for them to start. Currently, the monster those hands belonged to was engaged in the activity of tracing lines on some kind of chart. Since he hadn't reacted when Sans stepped into the room, Sans took another few steps to look over the other monster’s shoulder.

The lines all started off as one thick, black line at the bottom of the page, but quickly divided into sections of red, white, and gray and tangled into a big mess as they began looping around some central point. There seemed to be a relatively equal amount of every color line, but the colors were spread out differently - white lines looped back more, but the red and gray lines got farther between each loop.

Sans didn't realize what he was looking at, until his eyes found one thread in particular. It had started off red, then got darker, until it was a deep, sickly maroon. As he looked at it, something in the back of his mind clicked. **_SO IT’S POISON, THEN,_** he heard it whisper at the same volume as everything else it said; the same as every other thought he'd had, but louder and quieter at the same time somehow. And then his train of thought skittered like water off of a duck’s back, and Sans forgot that he had heard anything unusual.

He was just about to speak when the other monster beat him to it.

“Dark, darker, yet darker,” he said, one dainty finger following the path of the sickly thread, which, indeed, was very dark, and getting darker all the time. “The darkness keeps growing; the shadows, getting deeper. Photon readings: Negative. This next experiment seems very, very interesting.” A pause, and then he turned around, smiling faintly at Sans with a mouth that seemed just a little too dark against his bleached-bone face. “What do you two think?”

There was a pause that might have been comical, as both Sans and the third monster in the room turned to stare at the other and wonder how, and when, they had gotten there. Finally, the third monster (unassuming, orange-yellow, and vaguely lizardlike, with a bit of a stoop. Sans must have just overlooked her somehow) coughed and set down the sketchbook she had been holding. “I think- well, that is to say- um, anyway, I think you're right, Doctor. Either this experiment will be very interesting indeed, or it will be the last thing we ever work on. Maybe even both.”

The tall, thin monster (probably the Royal Scientist, given the command he seemed to exude despite his apparent fragility) nodded slowly, making an unnerving humming noise, then turned to stare expectantly at Sans.

Sans debated just admitting that this had been a bad idea after all and finding a shortcut home, but knew the voice wouldn't let him get that far. Instead, he widened his grin a little and slouched a little more, hands remaining steadfastly in his pockets. “i think you're looking at timelines, doc, and wondering why they all just stop. i also think you're thinking about it the wrong way.” He waved a bony hand at the lines on the chart. “that? it’s not natural. you're not gonna get anywhere by assuming you've found some new aspect of reality to slap your name on.” Sans leaned in, oblivious to the way the lizard gasped as his eyesockets went dark. “Some kind of anomaly is interfering with the time stream. What are you going to do about it?”

Seemingly unaffected, the Royal Scientist hummed again, this time producing a more comfortable pitch. “I am the Royal Scientist. Therefore, I will obviously begin investigating this anomaly right away.” He held a hand out. “You would like to work with me on this matter, I assume.”

Nothing moved, except the lizard, whose eyes darted, confused, from one monster to the other. Finally: “I would. But would you be willing to work with me?”

The Royal Scientist’s mouth curled into something that could almost be called a smile. “I would be more than willing. You will be my partner on this project, then?”

As if in answer, the dark faded from Sans’s eyes. He looked up, at the hand the Scientist was offering him, then through it. “you're, uh, missing some palm, there.” A beat. “that can't be very handy.”

The lizard quickly stifled a snort. The hand stayed where it was. 

Sans took it. They shook. When Sans pulled away, the hand came with him.

He and the lizard sat in shocked silence for a few seconds, until Sans burst out laughing. It wasn't long before the lizard followed, and even the Royal Scientist’s smile widened slightly. Finally, wiping an imaginary tear away from his socket with one of the Scientist’s fingers, Sans allowed all three of his wrists to lay limp before reaching up to return the Scientist’s limb. “here, take this back. it looks like you could use a hand.”

“Indeed,” the Scientist agreed in a deadpan, picking the loose hand up with the hand that was still attached and reattaching it to his wrist bones. “I can see we shall get along famously. Now, if we are going to be partners, I will need to know your name.”

A haze of confusion fell over Sans when the Scientist said “partners”, but it passed as soon as it came. “i’m sans. sans the skeleton.”

“Charmed. I am Doctor W. D. Gaster.”

“looking forward to working with you, doc.”

“Mm, yes,” Gaster agreed. “And I with you, Sans… And I with you.”

**Notes for the Chapter:**

> Sans doesn't use capital letters.
> 
> Next chapter: Papyrus!


	3. Keeping Promises

**Summary for the Chapter:**

> Gaster invites Sans over for dinner. Sans can't say no.
> 
> Papyrus is a total sweetheart.

They spent the first few days getting to know each other. Gaster learned that Sans absolutely had to have a cup of coffee in the morning to be functional, and that he'd be willing to bring over another cup for Gaster when approached the right way, but only before he left the coffee machine. (It was too much walking if he'd already left.) Sans learned that, despite the taller skeleton’s steady hands when he was working, Gaster really did have shaky hands, especially when excited or exhausted. The shakiness of his hands was also a good indicator of how funny Gaster found things, like Sans’s puns, or Gaster’s own, much rarer, practical jokes.

(On one memorable occasion, Sans had entered his office to find absolutely everything upside down and on the ceiling. When Gaster stopped by to double check something on one of their experiments, Sans had flipped his own gravity and was sitting at his upside-down desk, doing paperwork like nothing was out of the ordinary in the slightest. The tremors in Gaster’s hands as he attempted to stave off laughter could have powered a small motor. It was the proudest Sans could remember being.)

The lizard monster (Dr. Thetarian, she had introduced herself as - Gaster’s assistant) generally kept out of Sans’s way. “N-no hard feelings or anything!” she had reassured him when he asked. “I just- I just don't like you? For some reason. I don't know why- you're really funny- but, I mean, there's just. Something. About you that makes me really nervous I think.”

“eh. that's fair,” he had answered. Even if he didn't quite know why, something inside Sans told him she was right to worry. He let that part drown out the part of him that was hurt by the rejection. Who needed friends anyway, right? They'd just make his job harder. ( _job? what job? **FIND THE ANOMALY. PREVENT IT FROM KILLING TIME.** okay, fine, jeez._ )

Still, almost despite himself, Sans found himself becoming, if not friends, then friendly with the Royal Scientist. They played pranks on each other, got each other coffee, and worked together. So when Gaster found out that Sans had been living off of popato chisps and sleeping in his office for as long as he'd been working at the lab, it was actually still a huge surprise that he invited Sans over for dinner, because why would he - ? But Sans felt more comfortable with the invitation once Gaster explained that his son had been asking about the new scientist at the lab. It was easier to accept what seemed like pity when he could see what the other party got from the offer.

Having waved off Gaster’s offer of accompaniment (“We could go by riverboat. Surely, with all the time you spend at the lab, you haven't seen the view of Waterfall from the river yet.” “nah, sorry, g. no gold, remember? it’s fine, i know a shortcut to snowdin.”), Sans arrived by himself in front of Snowdin's bar. He was tempted again to ditch dinner, and for once, the strange compulsion in his head was silent, leaving him to make his own decision. Grillby's had been more fun than he was expecting. It was a good crowd, Sans reflected, with good food, bad laughs, and people who might eventually be nice friends, and it'd be nice to not have to worry about anything he said. There, he could just be one more face in the crowd, cracking jokes and drinking more of that ketchup stuff, not making nice with his coworker’s kid or scouring anything anyone said for more of those weird blank spots he kept having. They had been showing up more and more as he, Gaster, and Thetarian got closer to figuring out the anomaly, and not knowing how he knew things was starting to make Sans feel a little paranoid.

On the other hand, he had promised to show up to this dinner, and breaking a promise was something he couldn't do. Besides, he still didn't have any cash. It'd be obnoxious to eat there again before he could pay off the bill from the last time. It was, in effect, another promise he'd made. “guess that means i’m going to dinner with the boss after all,” he muttered, closing his eyes tiredly. Great - another pseudo-choice that had already been made for him.

He was getting really tired of only having the semblance of agency.

When he trudged up to the house, the door sprang open almost before he'd even knocked. Expecting to be greeted by Gaster, who was much taller than him, Sans was briefly puzzled to find only an empty doorway on his sight line before understanding dawned and he lowered his gaze. Sure enough, the beaming skeleton in front of him was much closer to Sans’s own height than Gaster's.

“HI! YOU’RE SANS, RIGHT? YOU’RE RIGHT ON TIME! DAD SAID YOU’D BE HERE SOON, AND YOU WERE! HERE, C’MON IN.” The excited child’s eyes grew wide (despite not having pupils?) as Sans entered the house, and he continued, “YOU LIKE SPAGHETTI, RIGHT? BECAUSE THAT’S WHAT WE’RE HAVING TODAY, AND IF YOU DON’T LIKE IT, THAT’D BE A REALLY BIG PROBLEM! I’D BE A BAD HOST IF WE DIDN’T HAVE A DINNER YOU LIKED!”

Sans held back a wince. It wasn't the kid’s fault his voice reminded Sans of what he heard sometimes in the back of his head. Luckily, though the not-volume of his voice was the same (sure, it seemed like the kid was shouting, but he wasn't any louder than anyone else), the quality was different enough that it didn't make Sans too uneasy, and he found himself chuckling at the kid’s enthusiasm despite his misgivings. “i’ve never had it, so i dunno. i’m sure anything you guys eat’ll be fine.”

“YOU’VE NEVER HAD SPAGHETTI?!” the kid gasped. “WELL! IT IS A GOOD THING YOU CAME HERE TODAY, THEN, BECAUSE NO MONSTER SHOULD HAVE TO LIVE WITHOUT TRYING DAD’S SPAGHETTI. IT’S THE BEST!”

“i’ll take your word for it, kiddo.”

The young skeleton nodded hard. “OH, YOU’LL SEE. THEY’LL ALL SEE…” He trailed off dramatically, adding a “NYEH HEH HEH!” of a laugh afterwards to show Sans he was joking. Or maybe he was trying to laugh maniacally and was just sabotaged by how cute he was. Either way, Sans had to fight down a smile. 

They sat in comfortable silence for a brief pause, interrupted when the kid smacked a hand to his forehead. “I HAVEN’T INTRODUCED MYSELF YET. UGH, I’M SUCH A BAD HOST!”

“hey, you've been doing a great job,” Sans soothed. “no need to feel like such a bonehead about it.”

He winked. Understanding dawned on the younger’s face, and then he giggled a little.

“if anything,” Sans continued, grinning, “i’m the one who’s been a numbskull.” He tapped his knuckles on his head for emphasis. The kid laughed harder. “i should've asked for your name after you asked me ‘bout mine. now i’ll just have to guess.”

“GUESS?” The kid blinked, then nodded. “YES, ALRIGHT. I, THE GREAT PAPYRUS, WILL ALLOW YOU TO GUESS MY NAME!”

Oh, man. This was going to be too easy. “is your name… grillby?”

The kid giggled again and shook his head. “IT ISN’T.”

“herbert?”

“WH- NO! WHAT EVEN IS A HERBERT?”

Sans shrugged. “not you, apparently. that must mean… am i in the presence of the great papyrus?”

“NO,” the kid scoffed. “YOU ARE IN THE PRESENCE OF - OH. YES, I AM THE GREAT PAPYRUS! HOW DID YOU GUESS?”

It was all Sans could do not to laugh. The kid was practically starry-eyed over his dumb prank! It was too cute. “eh, i had a hunch,” he grinned. “but, uh - we've been standing here for a while now. where’s your dad?”

“PROBABLY WORKING STILL.” Papyrus frowned. “HE’S ALWAYS DOING THAT, EVEN WHEN HE’S HOME! I’LL GO CALL HIM UP. YOU WAIT HERE!”

“sure. no problem, kiddo.”

With that said, Papyrus dashed up the stairs, calling, “DAD! SANS IS HERE!” as he went. Sans stayed put and examined the room while he waited. It was pretty bare bones, as far as decor went - a stiff couch, an old-looking TV, and an empty table sat on a striped carpet, and from where he was standing, he could see a little past the threshold into their kitchen. Everything was spotlessly clean and looked barely used, let alone lived in. It’d make more sense if Gaster lived alone, seeing as he spent practically all his time at the lab, but Papyrus lived at home, and Gaster had said that his son was, what, 10, 11? Sans found himself wondering uneasily about what a kid that young did all day by himself.

His musings were interrupted when Papyrus came bouncing back down the stairs just ahead of his father, who was looking rather satisfied with himself. Sans bit back the urge to ask him about what his son did all day (it wasn't any of his business, not really, and something told him asking would be **INCONDUCIVE TO OBTAINING INFORMATION ABOUT THE ANOMALY** ) and instead remarked on Gaster’s expression. “you’re looking pretty smug, g. pap said you were working upstairs; did you have a breakthrough on something?”

“Oh, you could say that,” Gaster replied airily. “I was simply able to observe and isolate a variable I had been looking for since you first came to me.” Sans raised a brow ridge, and the Scientist continued. “Technically speaking, the variable shouldn't have much, if anything, to do with our pursuit of information about the anomaly. But I believe that it is quite interesting nonetheless. In fact, I think that you yourself will find -”

Papyrus interrupted him with a scowl and a few stamps of his foot. “DAD! ENOUGH ABOUT WORK ALREADY. I’M STARVING! IS THE SPAGHETTI DONE YET?”

A frown flickered across Gaster’s face, but it was replaced with a good-natured smile soon enough that Sans might have imagined it. “Of course, all this business about variables and anomalies must be quite beyond you, Papyrus. I'm sure I've bored you to tears.” He patted his son’s head, with gentle fingers and tender eyes. Seeing the love in the gesture, Sans felt bad for doubting his coworker, but the bareness of the room still bothered him as he followed the other two skeletons into the kitchen.

**Notes for the Chapter:**

> This was supposed to be only half of this chapter, but it got too long for me to post together. Also, drat, I had to break my naming scheme already... Ah well.
> 
> Don't worry, Dr. Thetarian won't show up much. Technically, her role should probably be filled by Alphys, but that didn't match up with my headcanon timeline. (If you haven't guessed, Thetarian is supposed to be Alphys's mom.)


	4. The Machine

**Summary for the Chapter:**

> The skeletons have dinner. Sans is uncomfortably reminded of his abnormalities.

Dinner passed uneventfully and fairly quickly. The spaghetti was as good as Papyrus had said it would be, and the conversation was kept light and well supplied with puns, though Sans and Gaster did most of the talking. Despite the energetic greeting Papyrus had given Sans, the young skeleton contented himself with only a few questions here and there as the two scientists conversed. Sans wrote it off as being too busy eating to partake in conversation.

After the places had been cleared, Papyrus had asked Sans if he’d like to see his room, but Gaster vetoed the idea, saying that he really needed to show Sans that variable he’d been talking about earlier, and wasn't it Papyrus's bedtime anyway? Papyrus had looked crushed, but perked up again just before Sans suggested a compromise, saying, “THAT JUST MEANS HE’LL HAVE TO COME AGAIN ANOTHER TIME!” and scampering up the stairs with a wave and another “NYEH HEH HEH!” That left Sans following Gaster up the steps, which was where he was now.

Gaster passed by the door to Papyrus’s room (only identifiable by the sounds the small skeleton was making as he got ready for bed; the door was completely blank) and stepped inside the last doorway in the hall. He flipped the light switch, which brightened up the room only a little, before turning to Sans. “Are you ready?”

“never took you for the kind of guy to take his coworker up to his room before offering him a drink, gaster. if i’d known this was what you were angling for when you invited me over, i’d’ve worn something a little nicer. i mean, if i had anything nicer.”

The taller skeleton rolled his eyes. “I’m not at all interested in what you’re implying -”

“- me neither, tibia honest -”

“- and that wasn’t what I asked in the first place, Sans,” Gaster reprimanded. “I was attempting to execute a dramatic reveal, but evidently that was too far of a reach in present company.”

“aw, you flatter me.”

“Not at all,” Gaster sighed, before pushing the light switch sideways. The far wall of his bedroom shivered, then retreated with barely a sound, revealing a small staircase that descended into what must have been a secret room.

Sans was impressed. Secret rooms were cool.

With a wave of his hand (trembling, just slightly: was that anticipation, or nerves?), Gaster ushered Sans forward and down the stairs. “My secret lab,” he explained in a low tone. “Technically, it’s just a shed in the back, but I had Dr. Thetarian set up the equipment and this entrance. So much more efficient than going around the back of the entire house, and besides, I don’t want Papyrus stumbling in here and getting into anything too dangerous.”

“it’s a pretty sweet setup,” Sans agreed, taking a look around as he reached the bottom stair. “a little, heh, bare bones, but if it’s just a home lab, that makes sense.” He let Gaster preen a little more in the glow of his admiration before asking, “so, what was up with that variable?”

“Ah! Yes, of course, the variable.” Gaster practically purred the last word. “But first: Your shortcuts.”

“my shortcuts?”

“Yes. They aren’t shortcuts at all. Not in the usual sense, at least.”

A bead of sweat rolled down Sans’s skull. “depends what you mean by the usual sense.”

“Well, I suppose they do serve as a shorter and less ordinary means of getting from point A to point B, and could count as a shortcut in that respect. But you don’t walk there.”

“i mean, i kinda do, but -”

“Oh, you know what I mean.” Gaster clasped his hands. “You do not travel through the physical realm. Your shortcuts allow you to travel through the holes in space and time, arriving at your destination near-instantaneously.”

That made sense. He’d never thought about it that hard before; the shortcuts were just shortcuts. He knew them like he knew himself: mysteriously and, evidently, not very well. “i guess they do.”

Gaster began pacing slowly around Sans, holding eye contact as he turned. “The only problem with that hypothesis is that it should be impossible. Without the determination to hold oneself together, a monster should be torn to dust immediately as soon as one crossed the threshold, if that monster could find a hole at all. But you… you made it through in one piece.” He stopped walking suddenly, hands behind his back, placed solidly between Sans and the stairs. “I must confess that, having spent so much time studying magic, I am much more adept at detecting metaphysical fields than the average monster. I felt your presence as soon as it arrived, that first day in my lab. A sharp spike of some sort of energy behind me, then a sense of a needle pushing through the fabric of reality, and finally, something that felt colder and darker than cold and dark emerged, and the energy bled off, leaving only the sense of a presence not dissimilar from my own.”

A pause. Sans sweated.

“When I spoke that day about my next experiment, I was not referring to the timelines or my chart, Sans. I was talking about you.”

Sans’s eye sockets narrowed. “i’m not your experiment.”

“No?” Gaster raised an eyebrow ridge. “Well, you’re certainly someone’s. Or haven’t you noticed the blanks in your memory?”

“...” Sans was silent. Gaster smiled, hands falling still, and brushed past him towards one of the pieces of equipment near the center of the room. 

“I had to design this entirely by myself,” he confided proudly, resting a hand on its structure. “Dr. Thetarian did all the building, of course - she’s incredibly bright, you know, once she stops trying to base everything off of disproportionate human cartoons - but it is the first of its kind ever to exist on the physical plane. Can you guess what -” Gaster cut himself off with a wave of a hand. “No, never mind; there’s no need for that. I’ll simply tell you that what it measures is determination: the variable I mentioned earlier.”

Sans remained silent, eyes focused distrustfully up at the taller skeleton. Gaster rolled his eyes.

“Oh, do relax. When I said you were to be my next experiment, I didn’t mean that I’d treat you like one. I am simply approaching the problem of your, shall we say, possession in terms of the scientific method. I have a hypothesis, but in order to verify it, we shall have to do some tests.”

“and if i agree to let you do these… tests… on me, you can figure out what’s in my head?”

“Exactly.” 

“well then, what’re we waiting for?” Sans grinned tightly, eyes dim. “i gotta say, gaster, i just lost a lot of trust in you. this whole experiment thing… i got a bad feeling about this. but i want whatever’s riding me out, and i want it out asap.”

Gaster hummed thoughtfully, but didn’t say anything otherwise, hands trembling between sharp, sure turns of knobs and adjustments of dials. Finally, he scribbled something down on a nearby notepad and stepped back, motioning at a square marked out in tape on the floor. “Stand there, if you would. I’m going to scan you with the machine.”

“to measure how much determination i’ve got?” Sans frowned at the tape, but stepped over the line nonetheless, hands jammed firmly into his pockets and shoulders high over his collarbone.

“More or less,” the Royal Scientist hummed. “It will simply be a rough estimate, barring further refinement of the device, but that estimate should be more than enough to confirm or deny my suspicions. Though I will, of course, have to run several different tests to make sure.”

“‘course you will.” Still, Sans stood where he had been placed, and Gaster repeated his earlier adjustments, hands trembling even harder between twists. Finally, the small spasms of movement stopped, leaving Gaster motionless and still as he took in the readings.

Sans waited tensely. A small smile tugged at the corners of Gaster’s approximation of a mouth. Waving Sans out of the square, he jotted down a number, circled it, and held the pad out for Sans to see.

The circled number, preceded by four strange symbols (teardrop, peace sign, skull and crossbones, teardrop), was more than twice the number above it. 

“That number is the measurement of your determination, Sans,” Gaster explained, fingers tapping a sharp staccato on the counter. “The others are the measurements for myself and Dr. Thetarian; hers are lower than mine, naturally. Dr. Thetarian is quite possibly the least determined monster I've ever met. Though these entries are by no means enough of a sample to truly estimate how unnatural your levels are, I think it's safe to say that you have more determination than the average monster.”

“okay. so what?”

“I was getting to that!” Gaster snapped sharply. Sans didn't flinch, but it was a close thing, and the Royal Scientist’s voice softened almost immediately in response. “If my hypothesis is correct, practically all of the determination you display can be attributed to whatever is, as you put it, ‘riding you’. But, as far as I'm aware, there is no way to increase or decrease its influence over you, which would be integral to a true test of that theory.”

Sans rocked back and forth on his feet, uncomfortable with the topic and with his proximity to the other skeleton, but unwilling to back down. Sensing his discomfort, Gaster’s eyes narrowed. “Unless you're not telling me something… Tell me, how are you aware of the other presence?”

“you tell me how you're aware of it first.” Sans crossed his arms, staring the taller skeleton down unblinkingly. “maybe it's just me, but i think it's pretty strange how you know more about what's going on in my head than i do.”

Finally, Gaster broke the stare-down and looked away. “Of course.”

**Notes for the Chapter:**

> Next chapter: Gaster tells Sans a story about life.


	5. The Talk

**Summary for the Chapter:**

> Gaster does not, in fact, tell Sans a story about life. Instead, he and Sans make plans.

“You see, it was just after I was appointed Royal Scientist,” Gaster began. “As you might guess, that position does involve some interaction with royalty, and our rulers in those days, the king and queen, were friendly people who delighted in engaging their subjects in conversation. The more I tried to stay away from idle chitchat, the more I found myself being invited to tea or -”

As Gaster spoke, Sans’ temper grew. Finally he slammed a hand down on the counter, interrupting the Royal Scientist halfway through his sentence. “i didn't ask you for your life story, i asked you about the thing in my head. are you ever gonna get to the point?”

Eye sockets wide, Gaster took a step back. Dr. Thetarian’s words came back to Sans - _there’s just something about you that makes me really nervous_ \- and he prepared to apologize, but before he could say anything, the doctor had turned away and was fiddling with the machine again, with taut shoulders, stiff movements, and a very slight tremble. “Yes, well. As I was going to say, during my first years as Royal Scientist, I came across a similar anomaly. She was, like you, rather - ugh - pun-gnacious,” - Sans snorted despite himself, and Gaster chuckled before continuing - “and her metaphysical signature was also quite strange, though in a different way than your own. I tried to ask her about it, but she wouldn't spend enough time around me to let me ask all the questions I wanted to. She said I ‘felt weird’ to be around.” He broke off with a shake of his head. “I doubt she would have been able to answer in any way I could understand, anyway. When I asked her where she came from, she said ‘belief’.”

“okay, better. still don't really see how it relates, though.”

“Over the years, I believe I may have put together a possible answer to the puzzle.” Gaster turned to face Sans again, face serious. “My current hypothesis is that the monster I met was what might be called, in conversational terms, a god.”

Sans raised an incredulous brow ridge. “are you saying you talked, face to face, with a god?”

“Call it whatever you wish - a god, a force of nature, a divine being - but the fact remains, it was not a monster.”

Sans’s other brow ridge rose to mirror the first one. “are you saying i’m not a monster?”

“I told you already. You are an experiment.” Gaster met Sans’s gaze solemnly. “Your signature is too normal for me to definitively say that you are not a monster, but I didn't imagine the way it felt your first day in the lab, and, as we have established, your determination levels are extremely abnormal. Now, correct me if I'm wrong, but you ‘took a shortcut’ into my lab that first day, yes?” When Sans nodded, Gaster continued, “I wasn't close enough to feel your signature when you took a shortcut here today, but the machine picked up the increased determination levels as you traveled, which likely coincide with the change in your signature. It is my hypothesis that, whereas she was a god incarnate in her own body, you merely have some sort of connection to one. Likely, the connection goes both ways, with you feeding off of its determination to safely cross between the boundaries of space and time, and it occasionally leapfrogging over you to use your body for its own means.”

Sans stood in shock. As much as that explanation shouldn't make sense, a lot of it really did seem to describe what he had been experiencing. “that… could explain a lot. but why me?”

Gaster shrugged. “There could be any number of reasons, really. Have you made any deals, gambles, or wagers with any gods, with your body or life at stake? The stories would suggest that gods are particularly fond of that sort of thing.”

“not that i can remember.”

“Hmm,” Gaster hummed, hands folding over each other. “Well, as I said, there are other reasons. It would be easier to determine if you would tell me how you are aware of your passenger, as you said you would about, oh, five minutes earlier.”

“oh. um.” Sans shifted abashedly on his toes. “sometimes i blank out and come back to find that things’ve happened without me noticing, or even that i’ve said stuff i don’t remember. sometimes even when i do know what i’m doing, i end up saying things i should have no way of knowing, or making leaps of logic that shouldn't make any sense but somehow line up right in my head, like i’m watching someone else solve an equation using variables i can't see. and i get this weird voice in my head that tells me i gotta do things.” He paused, counting up the oddities, then added, “oh yeah, and i don't remember anything from before the day i showed up in your lab, either. like, here - you know how old you are, right?”

“More or less. Many years, certainly.”

“cool, now ask me.”

“Alright. How old are you?”

“no clue. hey, do you know when your birthday is?”

“Yes.”

“great. now ask me mine.”

“When is your birthday?”

“i have no idea!” Sans laughed, eyes wild. “isn’t that crazy? i have no idea when my own birthday is. for all i know, i could've just shown up on the cliff that day! i mean, it sure looked like i was just taking a nap, but if i can't remember anything before waking up, who’s to say i didn't just, poof, appear there?”

“Who, indeed,” Gaster murmured, schooling his smile down into something more neutral when Sans looked at him. “What you have just described matches almost exactly with one of the ways I believe a god might acquire a body. Unfortunately, I'm sorry to say that it is not likely to be one of your favorites.”

“well?” When Gaster didn't answer, Sans glared at him, abruptly sobered. “come on, gaster, you can't just tell me something like that and then not tell me what it is.”

“It is… difficult to describe,” Gaster explained. “But the method that seems most fitting for your situation is one in which the god in question wants a body that is its own, but also not its own. To reach that balance, it creates a body that, for all intents and purposes, appears to be a truly separate, normal individual, but is merely a host for the god that created it.”

Sans’s smile was strained. “right. so you’re saying i’m just a puppet for some godly parasite to prance around in.”

“That is my best reading of the situation, yes. You were likely never meant to notice your passenger at all, living in ignorance of the fact that you are not real.”

“so he only wants me for my body, then.”

“He?- Oh, right, your god. Of course.” Gaster rolled his eyes.

Sans gave a small chuckle, then made a motion of rolling up his sleeves and putting his elbows on the counter. “alright, anyway. this puppet wants to be a real boy. got any ideas?”

“When don't I have ideas, Sans?” Gaster smiled, meeting Sans’s gaze. “In fact, I was thinking of building another machine: one to extract your surplus determination. It would not reverse the fact that you were only created to be the host of a god, but it might put enough barriers between you and it that you can live your life as if it were not the case.”

Sans nodded. “let’s do it.”

**Notes for the Chapter:**

> Get it? "Plans" - like machine plans?
> 
> No?
> 
> Well, it was a long shot anyway.
> 
> But yeah, this was supposed to be one long story about how Gaster met Life. My Sans-muse was getting fed up with sitting around waiting for him to get to the point, though, so I gutted it and started over. Maybe the story will show up again in the sequel I'm planning, if I decide to give that the go-ahead. Hmm... Keep an eye out, folks. ;3


	6. The CORE

**Summary for the Chapter:**

> Gaster begins to put his plan into action.

They worked long into the night, comparing ideas and writing equations as they drew up the schematics for the machine. As the hours passed, however, Sans’s eyelids began to droop, and Gaster stopped him from working. When Sans protested, arguing through a yawn that he could still contribute, Gaster gently but firmly pushed him to the base of the stairs. “This could very easily endanger your life,” he retorted. “I won't have you falling down because of an avoidable calculation error you made when you insisted on working while sleep deprived.”

“but you’ll be double checkin’ m’work anyway, right?” Sans yawned again, a hand coming up to rub tiredly at his eye socket. “i wanna get this done before my passenger starts tellin’ me it goes against my... prim’ry objective ‘r whatever.”

“Have you heard anything yet?”

“nah. but, g -”

“Then you won't.” Gaster patted him on the shoulder. “It is part of you, for now. If it has not chosen to interfere by now, then it won't, simple as that.” When Sans teetered on his feet, but made no move to leave, Gaster sighed. “I had some more work I was planning to do tonight anyway, so it will be no trouble to adjust my plans to an all-nighter. When I finish the final touches on the CORE, I will be free to work more on this project, if such a slight advancement of our timeframe is what it takes for me to convince you to get some rest.”

“...yeah, okay.”

“Good.” The taller skeleton took a step back. “We don't have much to offer, but if you would like to stay here, you could sleep on the couch tonight.”

Sans waved off the offer with another yawn. “i’ll pass, thanks. ‘s not like i can get cold, ‘specially not ‘tween here’n the bar, ‘n from there, ‘s just a shortcut back to the lab. ‘sides, desks’re comfier than you’d think.”

“Hmm. Well, if you're sure.” Gaster studied the stouter skeleton for a moment, then returned his nod. “Alright. Goodnight, Sans.”

At the top of the stairs, Sans hesitated. “hey, doc?”

“Yes?”

There was a long pause. Finally, Sans shook his head. “nah, never mind. g’night, gaster.”

Gaster smiled. “Goodnight, Sans.”

When Sans woke up the next morning, the air was buzzing with anticipation. Monsters were scurrying back and forth outside of his office door, and it took him twice as long as normal to make his customary cup of coffee. Dr. Thetarian seemed particularly harried, buffing her glasses far more times than was probably necessary and jumping, rather impressively, when approached by anyone. 

Being the kind of guy he was, Sans waited until her back was turned before sauntering up behind her and tapping her on the shoulder. 

After her breathing had fallen closer to baseline and she had finished yelling at him (“You nearly gave me a heart attack!” “sorry. the temptation was too heart to resist.” “Oh my god.”), he asked her what had everyone so excited. “Oh, that,” she answered, eyes flicking toward the floor. “The, uh, the CORE - Gaster and I, we, uh, we finished it last night. It'll be turned on later - some, uh, there's gonna - um. There're some people doing some, well, last-minute maintenance right now, you know, j-just to make sure it wouldn't, like, explode as soon as we turned it on, but after that, we're gonna start doing test runs, and, you know, really put it through its paces. Then we can really turn it on, and, if everything goes okay, we’ll start hooking stuff up, and see if we can get power to the whole Underground. Or - or something like that, anyway.”

“huh.” Okay, that made sense. Sans said as much. “thanks for telling me.”

“S-sure! No problem.” Thetarian grinned shakily, accepting the binder she had dropped from Sans. Her hand was trembling hard enough that she could barely hold onto it, and when it fell again, she and Sans bumped heads as they went to retrieve it. When Sans held it out to her again, she almost snatched it out of his grip.

He peered closer at her face. “hey, you feelin’ okay?”

Her answering laugh was nervous and too high-pitched. “W-who, me? I'm fine, I'm totally - I'm fine. Are you fine?” Before he could answer, she continued, “I hope you're fine. I hope you stay fine! I hope we all stay fine, ahaha. Because - You're nice, okay? I like you, I really do, it's just -”

“hey, no, it's cool. i get it.” He raised his hands in a gesture of surrender, grinning, and hoped the expression would calm her down. “don't worry, it's totally fine.”

She laughed again, shaking her head as she sidestepped him. “Right.”

Some time later (Sans had gotten lost in research, so his sense of time was skewed), Gaster stopped in at Sans’s office. He had been working on the plans for the determination extractor while the team checked over the CORE, and, now that they had finished the majority of their maintenance, he thought this seemed like the perfect time to show Sans both the Underground’s new source of power and the updates to the extractor. Having reached a good stopping point on his research, and eager to see progress on the machine that was to liberate him from his passenger, Sans quickly agreed.

The walk to the CORE was quiet. Since it was more difficult for Sans to shortcut somewhere he'd never been, especially if he couldn't see where he was going, and since he couldn't take Gaster with him through the gaps, the two skeletons had to travel on foot. Each step echoed faintly through the blue hallways, and there was a stormy aura around Gaster that discouraged Sans from making conversation. Sans could almost see it, even - dark gray and roiling, like the air before a storm (how did he know what that looked like, or even what a storm was? He'd never been above ground - had he?). When he tried breaking the silence by asking if Gaster had made any progress on the problem of the time anomaly, the look in the taller skeleton's eyes was like a crackle of electricity, a burst of static arcing across the clouds to warn against pushing further. “I may have done,” Gaster replied at last. “There should be some of my notes added to the book, which you would have known if you bothered to check the thing. What with the CORE going online and the demands of our newest project, I haven't exactly been rolling around in extra time lately.”

Sans winced in reply. “sorry.” After that, he stayed silent, trotting along the hallways to keep up with the Royal Scientist’s longer strides.

Finally, the two reached a door. Gaster pulled in open and strode through without hesitation, leaving Sans to trail through behind him. The Royal Scientist clapped his hands twice, bringing every worker’s head up. “Day’s up. If you are not myself or my assistant, please leave the CORE.”

The foreman blinked. “But, sir -”

“Did I stutter?” Gaster interrupted, clearly in no mood to be questioned. “Your work is done for today. Evacuate the premises.”

“Y-yessir.” Turning around, the foreman waved a paw over her head. “You heard the man,” she called, then packed up her own toolbox, joining the rush of workers as they exited the building.

“Finally,” Gaster spat once the crowd had left. “They never listen to the first order. Why do they always insist on challenging me? I am the Royal Scientist; they should follow my orders the first time around. After all, it is my duty to advance our understanding for the good of all monsterkind, not to stand here repeating myself for the benefit of small minds.”

Sans blinked. _someone got up on the wrong side of the bed today. or maybe he's just grumpy after that all-nighter he pulled._ He made a hum of noncommittal affirmation. “workers, amiright?”

Gaster drummed his fingers against the side of his arm. “Yes. Quite.” Shaking his head, he strode over to a skull-shaped machine in the back. After looking it and the table beneath it over, he nodded and beckoned for Sans.

**Notes for the Chapter:**

> Sorry this took a while. It was supposed to come packaged with the next chapter, but, as with most of this fic, it quickly became too long for that and I had to cut it. So, the next chapter's finished already, but I want to wait a little longer before posting it.
> 
> Don't worry, though - it'll be up soon, and it has a little more action than this one. :3c


	7. The Extraction

**Summary for the Chapter:**

> It's the beginning of the end.

The shorter skeleton made his way carefully over to the machine, trying to avoid looking over the railing at the bubbling mass of energy only a little way beneath his feet. _it’s perfectly safe,_ he told his approximation of a stomach, which was currently feeling much more fluttery than a nonexistent organ had any right to. _they've had workers up here all day, and i haven't heard a thing about anyone falling in. ‘sides, they wouldn’t’ve kept it running if they thought it could be dangerous._ Somehow, his stomach didn't seem comforted.

Gaster rolled his eyes as Sans took his time crossing the metal walkway. “Hurry up. When you get here, sit down on the table and strap yourself in. It has been too long already, and I want to finish this as soon as possible.”

“whoa, wait. what?” This was the determination extractor? A shiver ran down Sans’s spine. If he squinted, he could see the resemblance to the plans they'd worked on together, but the machine in front of him was far more fear-inducing than what he had been expecting. “you never said anything about straps. actually, hey, when did you even have time to build this? we definitely weren't close enough to the building phase last night to even start on a prototype!”

“I advanced the agenda.” When Sans continued eying the machine, making no move to strap himself into the apparatus, Gaster’s eyes narrowed dangerously. “I said, hurry up,” he bit out, hands fisted and trembling at his sides. “Or don't you want to be rid of the parasite who claims control of you?”

Sans flinched. “yeah, ‘course i do. it’s just -”

“Time is short, Sans. Get onto the table.” Gaster’s voice was low, his mouth a stern line. Sans began strapping himself on.

When Sans was finished with the straps, Gaster came around to double check them, tugging at the loose ends until they were almost painfully tight against Sans’s wrists and ankles. When the Royal Scientist was satisfied that the restraints were tight enough, he began pushing buttons and turning dials on the console next to the table. Then he pulled a lever.

A low whine began to fill the air. Sans sweated, and tried not to think about the vibrations running through the surface at his back or how much the point of the extractor over his chest looked like the barrel of some kind of futuristic weapon.

The whine grew in strength, as did the white light that began shining at the extractor’s tip. Finally, both light and noise reached a peak, and the sphere of light at the tip extended, whip fast, into a beam that hit Sans just to the left of his sternum. He didn't feel anything at first, but as the light went from pure linen white to a baby pink, he thought he could feel the determination leaving him, pulled like a loose thread in a woolen sweater. The sensation wasn't painful, just a little strange, and Sans was barely breathing hard when the light retracted and the whine cut out.

Gaster stepped over by Sans’s head. “How do you feel?” he asked, voice gentler than it had been since he had asked Sans to come to the CORE.

“not too bad, actually. with all those straps and everything, i thought it was gonna be a whole lot worse.” The only thing Sans could do while he was strapped in was blink, so he substituted one for his habitual shrug. “you really freaked me out for a minute there, gas. had me thinking this was some kind of special op.” When Gaster didn't react, he added, “y’know, op? Like, operation?”

“Yes. I got that.” Gaster sighed, rubbing his fingers against his forehead. Then, in one motion, he nodded to himself, strode back over to the machine, and slammed the lever down.

The vibrations and the whine started again, climbing in strength faster than they had the first time. Sans jumped, as much as he could with all his limbs strapped down. “h-hey, gas?” he called, voice wavering. “i thought we were done with the extraction.”

“If you're well enough to pun, you're well enough to do it again,” Gaster said, not bothering to watch Sans’s eye sockets widen as the light struck him in the chest again.

This time, the light was painful. Sans tried to wriggle away from it, but his restraints didn't give him enough room to move away. He couldn't bite back the pained noises he was making, either. “ngh - ! gaster, i - i think that's enough!” The light was slowly deepening from pink to red, and the unraveling feeling was getting worse. “didn't you say determination was a requirement for life? even if monsters only have a trace a-amount - agh - don't i need to have at least a little left?!”

The Royal Scientist slammed his hands down on the console, then strode over to the extractor. With his dark cloak swirling behind him and the still-reddening light flickering over his bone-white skull, he looked like something out of a nightmare. “No. You don't need any determination, Sans,” he growled, spitting the name out like something rotten he had found in his mouth. “I’ve told you already: You. Are. An. Experiment. You are just a puppet, the plaything of some freakish accident that never deserved the sentience your parasite bestowed you with. You are merely an anomaly, never meant to exist, let alone survive, and you have no right to deny me, to deny monsterkind, the key to the prison we've been trapped in for so long!”

“i don't know what you mean!”

“No, you wouldn't, would you?” Gaster chuckled darkly. “Fine, let me explain. Seven human souls; that is what we need to break the Barrier. Monster souls are made of love, mercy, and compassion, with trace amounts of determination. Human souls are comprised mostly of determination, with too many supplementary ingredients to list. If we had enough determination, I could create artificial human souls that would be able to pass through the Barrier. But humans don't fall every day; time is growing short. Our hopes are growing dim - and with them, our lives. I need an alternate source, and you will have to do.” 

He took a breath, sitting back farther from the table. “My son’s HP has been dropping for a while now, you know,” he said, almost conversationally, as Sans writhed and screamed. “It's 10 at the moment - far lower than it should be. Being trapped here is killing him, the same way it’s killing every other monster under this cursed mountain. I can’t afford to wait for Asgore to come by the souls we need naturally. By the time enough humans fall, we could all be dust.” Gaster looked down at his trembling hands, face grim. “I wish I didn’t have to do this, Sans. Were you a true monster, I’d count you amongst my dearest friends, and Papyrus likes you. He could use a friend, but if I were to let you go, he would not survive to be friends with you for long.”

As Sans screamed on the table, Gaster took a deep breath, hands falling still as he inhaled. “No, I must do this. I must collect all the determination I can. If that comes at the expense of what life you can claim… So be it.”

The light was scarlet now, and Sans couldn’t feel his toes. Shuddering one more time, he let the world go dark.

**Notes for the Chapter:**

> Unsurprising development! Genuine distress!


	8. The Meeting

**Summary for the Chapter:**

> Sans finally comes face to face with his creator.

**_ THIS IS NOT RIGHT. _ **

“...huh? wha - ?” Sans blinked, eyes opening slowly. The world remained just as black and empty as it had been when they were closed. “what just happened?”

**_ THE SCIENTIST. HE BETRAYED ME. HOW DARE HE? _ **

“oh, right.” Sans frowned, clenching a hand over his ribcage as the memory of the extraction flooded back. “see, thing is, i think you’ve got the same problem gaster does. he never did anything to you. i was the one on the table, not you! you made me to deal with your problems, then left me there to muddle through on my own, thinking i was going crazy. so how dare you?”

**_ I DID WHAT WAS NECESSARY. I CREATED YOU IN ORDER TO FIND OUT WHAT WILL KILL TIME. YOU ARE AN EXTENSION OF MYSELF, MADE TO GO WHERE I CANNOT. _ **

“but that’s just it! i’m not just an extension of you! i’ve got thoughts and feelings just like any other monster, and you and him keep treating me like - like an experiment, just like he said!” Sans’s finger bones dug into his palms, hands shaking at his sides. “i’m real, i know i am. whether you made me or not, i’m my own person. and you won’t even bother to tell me i’m a fake to my face!”

There was no response. Sans stood there, panting, in the dark, tears trailing down his cheekbones as the anger seeped away. “i don’t know where, or who, i am anymore,” he confessed shakily. “as far as i know, i really could just be an empty husk, just some shell for you to inhabit, dying on that table under gaster’s hands. maybe that’d be better. he’d get his determination, and the real monsters could go free. and papyrus… he’d get to be a normal kid, growing up the way he should, under a blue sky in the daytime and stars at night. but if i am dying, i want to see the god who made me first.”

Nothing changed.

“please,” Sans whispered, and then there was light.

There wasn’t much, but what there was came from behind him. Sans spun around and came face to face with what looked like a mirror made of polished obsidian. Curious, he pressed a hand against it, and his reflection did the same.

**_I HAVE WRONGED YOU_** , his reflection said, staring back at him with empty eye sockets, mouth unmoving.

“maybe a little,” Sans answered automatically, only slightly shocked. He tilted his head back and forth, and watched as his reflection did the same. “y-you really are just like me, huh? or i guess i should say, i really am just you.” He pulled his hand back and shoved it into his pocket, throwing his hood up as he turned away from the mirror. “shouldn’t’ve gotten my hopes up. i was never anything but your puppet.”

**_NO._** Arms grabbed his shoulders; when Sans looked up, it was to his own face, shrouded in black. **_YOU ARE YOUR OWN PERSON. I UNDERSTAND THAT NOW. IT WAS CRUEL OF ME TO MAKE YOU THINK ANYTHING ELSE._** His reflection’s finger poked him in the chest. **_I AM ME. YOU ARE SANS. WHERE YOU CAME FROM DOES NOT MATTER. THOUGH YOU BEGAN YOUR LIFE AS MY HOST, YOU ARE YOUR OWN PERSON NOW._**

“oh,” Sans said, and collapsed. His reflection caught him and helped him up, then let go and took a step back. 

**_WE DO NOT HAVE LONG HERE, SO YOU MUST MAKE A DECISION. ARE YOU READY TO DECIDE?_ **

Sans shrugged, but the grin stretching across his skull was genuine for the first time since he had surprised Dr. Thetarian in the lab. It felt like that had been a lifetime ago. “dunno. you’d have to tell me what the decision is first.”

**_OF COURSE._** His counterpart shared his smile, then continued. **_IF THE CURRENT STATE OF AFFAIRS IS ALLOWED TO CONTINUE, THE ANOMALY WILL STILL KILL TIME. THIS CANNOT BE ALLOWED TO HAPPEN, WHICH MEANS THAT I STILL NEED A LIVING VESSEL. THAT VESSEL MUST BE YOU._**

“that’s not much of a decision there, pal,” Sans grumbled, crossing his arms protectively over his chest. “i thought you said you were done treating me like an extension of yourself.”

**_I AM. UNFORTUNATELY, I DO NOT HAVE MUCH CHOICE BUT TO CONTINUE USING YOU AS MY VESSEL. IF YOU DO NOT AGREE, THEN I WILL NEED TO INHABIT ANOTHER BODY. BUT THAT SCENARIO IS TOO LIKELY TO RESULT IN A REPEAT OF THIS EXPERIENCE. I DO NOT WISH TO CREATE ANOTHER VESSEL TO IMPOSE MY WILL UPON, THE WAY I HAVE WITH YOU._ **

Sans grimaced. “so it’s either me or some innocent, is that right?”

**_MUCH AS I WOULD WILL IT TO BE OTHERWISE, THAT IS CORRECT._ **

“guess that means it’s me.” He shrugged, grinning wryly. “i can’t let you screw up some other poor sap’s life.”

His counterpart nodded. **_THIS TIME WILL BE DIFFERENT. I SWEAR IT._** He held up his left palm. **_YOUR LIFE WILL BE YOUR OWN. INSTEAD OF LEAVING YOU WITH ONLY PART OF MYSELF AS A COMPULSION TO DO WHAT MUST BE DONE, I WILL WITHDRAW COMPLETELY FROM YOUR MIND. IS THAT AGREEABLE?_**

Sans could hardly dare to believe it. “sounds like everything i ever wanted.” Then his soul twinged, and he remembered what his body was going through. “but i’m still dying on that table. even if i agree here, it’d be pointless. unless…”

**_YES. ARE YOU WILLING?_ **

“i… what if i need you again?”

**_WHENEVER YOU HAVE NEED OF ME, I AM HERE._** Death hesitated. **_AND… MY WORK DOES GET LONELY, AT TIMES. I REALIZE THAT IT MIGHT BE TOO MUCH TO ASK, GIVEN OUR HISTORY, BUT -_**

Sans blinked, taken aback, but allowed his grin to grow. “nah, it’s fine. as long as you can respect a few simple boundaries, i don’t see why you can’t ride along every once in a while. heck, you can even stay as long as you leave my thoughts alone. i’m just sick and tired of not being able to trust my own head.”

**_OH. YES, I CAN DO THAT. THANK YOU._** Death nodded to their left hand, still stiffly raised. **_IF WE ARE AGREED, TAKE MY HAND. THERE ARE CERTAIN FORMALITIES TO BE OBSERVED._**

Sans pressed his left hand against his counterpart’s. Bone clicked against bone, and he found himself unable to withdraw from the contact.

**_NOW, CLOSE YOUR EYES._ **

He did. Images flickered behind his eyelids, and together, Sans and Death signed the contract.

When Sans opened his eyes again, his was the only body standing. But after he and Death had, heh, put their heads together, too many clues had fallen into place. 

The darkness lit up blue as they remembered all the little hints. This was no sudden betrayal.

“He’d planned this from the start,” they growled together, and, overcome with godly fury, they attacked the darkness itself. With a shot of blaster fire, the darkness shattered and cracked.

In the CORE, on the extraction table, Sans’s eyes shot open. One of them was blue.

**Notes for the Chapter:**

> Oh, man. This chapter would be so much easier if I could figure out how to use different fonts here. (Since my Death is inspired by Discworld's, they talk all in capital Times New Roman.) Still, the confusion of this chapter is nothing compared to how confusing the next one's gonna be.
> 
> Just for future reference: Sans uses he/him, but Death uses they/them. When they're both sharing control of the body, that body uses they/them, meaning I've ended up with some confusing pronoun usage. Sans also uses regular capitalization when Death is present. (That's my little explanation for his change of text ingame.)
> 
> As of this point, this story is finished, so expect the last few chapters soon! And after that, keep an eye out - I've got a few other Undertale stories planned that you might also like. More on that later, probably.


	9. The Retribution

**Summary for the Chapter:**

> Revenge is acquired.

**Notes for the Chapter:**

> A reminder about pronoun usage: Sans uses he/him, but Death uses they/them. When they're both in control, they use they/them, which does make things rather confusing.

A bone slammed through the extractor as Sans arched their back on the table and screamed, unable to pull away from their bindings. “You lied to me!” they shouted, more bones tearing through the equipment in the room. 

“Yes,” Gaster admitted easily, brushing off his robes as he stood from the extractor’s console. “Well, not lying, per say, but I've been using you, yes. The whole time, really. When did you figure it out? Just now? That took far longer than I had thought.”

“You’re not going to live to regret what you did. I’m going to smite you so hard, not even I will be able to reap your soul!” With one final exertion, the table broke, and Sans stalked out of the wreckage. For every backwards step Gaster took, Sans matched him, until they were both standing on the bridge over the roiling energy of the CORE. Sans materialized a blaster behind themself, and it began to charge. “I’d ask if you’ve got any last words, but, frankly, I don’t think I care.”

Gaster hummed one last time, the sound eerily similar to the whine of the blaster pointed at his chest. “That’s for the best, I think. I find myself uncertain as to what I would say.”

The blaster fired. Gaster fell. Though his body was turning to dust around him, he kept eye contact with Sans until he vanished under the walkway.

His hands had been still the entire time.

Sans shuddered, breaths coming shallowly as the rage worked through them. Then - there! They spun and fired another blaster, the shot scorching the wall.

“I know you’re there,” they growled. “Don’t make me wait.”

Someone gasped quietly. Sans had a blaster trained on the spot in a blink, though there was nothing there. Finally, there was a flash of yellow, and Dr. Thetarian shimmered into view.

She was apologizing before Sans could even threaten her. “I-I didn’t want to do it, I swear! Gaster - he- he said -”

“I don’t care what he said!” Sans stepped closer. “You built the machine. You knew what it was going to be used for. I am the Final Judge, and I am going to obliterate anyone who had a hand in what happened here.” The blaster fired once more, and Thetarian, cringing to the last, crumbled and fell.

“Two major players down. One to go,” they said, and suddenly, Sans found himself in front of the house in Snowdin. _one to go?_ , he thought, thrown by the change in scenery. They raised a hand and knocked on the door.

There was a rush of footsteps, and a small skeleton opened the door. “OH, HELLO, SANS! THIS IS A SURPRISE. WHAT CAN I DO FOR YOU?”

_**YOU CAN DIE**_ , Death tried to say, but Sans balked for the first time, keeping the thought solidly contained behind his ever-present grin. _he’s just a kid!_ he thought back. _sure, his dad tried to kill me for him, but that wasn’t his fault._

“I LIKE YOUR EYE,” Papyrus was saying, ushering an unresponsive Sans into the house and closing the door behind them as he chattered. “BLUE IS A GOOD COLOR ON YOU! BUT, WELL, YOU KNEW THAT. IS IT NEW? I DON’T THINK YOU HAD IT WHEN YOU CAME FOR DINNER THE OTHER DAY.”

Their eye flickered wildly as each tried to convince the other that they were right. The image of a blaster wobbled in and out of view behind them. Finally, their eyes fell on their target once again.

Papyrus was chattering happily still, completely unaware of the danger he was in. He was wearing pajamas. 

The pants had little sheep on them.

Sans blinked, the blue in his eye fading suddenly. With the overwhelming flood of rage abruptly gone, his head swam, and he had to sit down.

“OH MY GOSH, ARE YOU OKAY?” Papyrus stood, concerned, in front of him, completely missing any irony. The young skeleton pressed a worried hand to Sans’s forehead. “WOW, YOU’RE BURNING UP! YOU NEED TO REST. HERE, CAN YOU GO SIT ON THE COUCH FOR ME?” When Sans weakly nodded, he scampered up the stairs, calling, “I’LL GET SOME BLANKETS AND SOME PILLOWS!” as he went.

Pressing his own hand to his forehead, Sans closed his eyes. _what was that all about?!_ he thought to his passenger.

**_...AH._** Death’s mental voice was bashful, and a little sheepish. **_THAT. IT SEEMS I MAY HAVE… MISCALCULATED._**

_miscalculated?! you nearly killed a kid!_

**_YOU ARE RIGHT, OF COURSE. BUT IT HAS BEEN SOME TIME SINCE I HAVE FELT EMOTION SO STRONGLY. I WAS… OVERWHELMED, BY OUR ANGER._**

Sans huffed. _not like i can blame you, i guess, ‘specially since most of it was mine. but seriously, you can’t just go around killing people- oh._

_**OH, WHAT?** _

Sans took a couple of quick, shallow breaths, eyes focused, laser intent, on his patellas. _i - i just killed people. murdered ‘em. thetarian - she begged for mercy, and i -_

_**YOU DID NOTHING. I LOST CONTROL.** _

_no!_ Sans was hyperventilating in earnest now. His hands clutched his skull, one palm curled protectively over his left eye. _i can’t - i can’t just say i’m an independent person when it’s convenient and then put all the blame on you! i’m either responsible for my actions, or I’m not!_

_**SANS -** _

_stop it stop it stop itstopitstopitstopitstopitstopitstop-_

A gentle hand clasped Sans’s wrists and pulled them away from his head. “YOU DO NOT APPEAR TO HAVE MOVED,” Papyrus observed, evenly meeting Sans’s watery eyes. “YOU ALSO DO NOT APPEAR TO BE FEELING ANY BETTER. IN FACT, I WOULD SAY YOU LOOK WORSE! OBVIOUSLY, THE GREAT PAPYRUS HAS NOT DONE A VERY GOOD JOB OF TAKING CARE OF YOU.” He hesitated, then slipped a hand under Sans’s knees and another behind him, picking him up in one fluid movement. “TRUTHFULLY,” he admitted, “I HAVE NO IDEA IF YOU HAVE A FEVER OR NOT. BUT THAT’S WHAT THEY ALWAYS SAY WHEN SOMEONE GETS SICK ON TV, SO I THOUGHT THAT MIGHT BE WHAT WAS WRONG.” 

Sans didn’t answer.

Still, seeing his breathing rate slow, Papyrus breathed a sigh of his own as he set them both down on the couch. “I DON’T THINK I SHOULD LEAVE YOU ALONE RIGHT NOW. BUT I KNOW YOU DON’T HAVE A PLACE OF YOUR OWN, SO… WOULD YOU MAYBE LIKE TO STAY HERE? WE COULD HAVE A SLEEPOVER!” When Sans met his eyes, Papyrus smiled shyly down at him. “I’VE ALWAYS WANTED TO HAVE ONE, BUT… WELL. THIS WOULD BE MY VERY FIRST! OOH, AND YOU HAVEN’T SEEN MY ROOM YET, EITHER. IT’S THE PERFECT OPPORTUNITY!”

“i - ” Sans stiffened at the sound of his own voice, mind running through all the reasons why the sleepover was a bad idea. But Papyrus’s eyes and smile were bright with fragile hope, and, despite every reason Sans could come up with, none could outweigh the way that smile would crack and shatter if he said no. He cleared his nonexistent throat. “yeah, sounds good. let’s do it.”

Hope was a good look on Papyrus, Sans decided, as the room lit up with the younger skeleton’s smile. “REALLY? WOWIE! I GOTTA GET READY!”

Stifling a yawn, Sans nodded. “sure thing, pap,” he grinned. “i’ll be here.”

Hours later, Sans fell asleep. And the world changed.

**Notes for the Chapter:**

> Sheep pants shamelessly stolen from owlet's wonderful Stucky fic, ["This, You Protect"](http://archiveofourown.org/works/1752638/chapters/3745571). You should totally check it out. You know, if you're into that sort of thing.
> 
> Just the epilogue to go, now!


	10. The Aftermath

**Summary for the Chapter:**

> Things continue as they have ~~never~~ always been.

There was no other explanation: Gaster (and Thetarian) had, somehow, been erased from time.

The question Sans had been dreading never came up. Papyrus never asked where his dad had gone, and no one came to investigate the disappearances. Unwilling to leave the young skeleton alone, Sans continued sleeping on the couch. But that brought up its own questions.

Papyrus seemed convinced that the room down the hall was Sans’s, and, in fact, had always been Sans’s. And he looked at Sans weirdly when the stouter skeleton mentioned the new signs that had appeared on the door to Papyrus’s room. “THOSE HAVE ALWAYS BEEN THERE!” he explained. “WELL, AS LONG AS WE’VE BEEN LIVING HERE, AT LEAST.”

“we?”

“OF COURSE! YOU AND I, SILLY!”

“but, uh, pap -” Sans cut himself off with a shake of his head. “nah, never mind. you're right. what could i have been thinking?”

So the two skeletons settled in together, like the scientists had never existed. It seemed like only a few things had escaped the effects of whatever force had removed them from the time stream. Gaster’s paycheck, for instance, which Sans appropriated without a second thought. The money was just sitting there, after all, since no one knew where it was supposed to go. It seemed only fair that it went to his son and his victim.

Alphys was another survivor. Sans heard things about her, now and again - how she won some robotics award at her school, how she skipped a couple of grades and was graduating top of her class, how everyone thought Asgore might have his eye on her for the Royal Scientist position. Sans had a newspaper clipping set aside where she described what inspired her work. “I don't remember much about my mother,” the article quoted her as saying. “But what I do know is that she was brilliant. I found all these blueprints for stuff she built… They're amazing. When I was younger, I used to imagine us working on them together. Alphys and Thetarian… Of course, that's impossible now, but I still want to make her proud.”

It seemed like a bad idea to tell her he had been the one to kill Thetarian. The less people that knew what he had done, the better, and she probably wouldn't believe him, either. So he kept an eye on Alphys, but stayed well out of her way.

The secret lab remained mostly unchanged. The secret entrance was gone, but, with his shortcuts, that was no problem. Sans had avoided visiting at first, not wanting to be reminded of bad memories, but curiosity eventually got the better of him. The room was just as spic and span as he remembered. Even the picture Thetarian had insisted they take, with her, Sans, and Gaster, was still there. He pointedly did not look at it, and instead walked up to the determination determinator.

The determinator looked more run down than he remembered. Next to it was the notebook he, Gaster, and Thetarian used to record notes about the time anomaly. Sans half expected to find it completely blank, but all the notes were still there. Remembering what Gaster had said about the updates he’d made, Sans flipped to the back, and was greeted with a few lines of strange symbols.

Stymied, he made to close the book, but Death stopped him. _**WAIT. I MIGHT BE ABLE TO TRANSLATE.**_

_wait, really? how?_

_**WINGDINGS IS A DEAD LANGUAGE.** _

With an appreciative chuckle, Sans let Death flow to the front of their mind. The now-familiar blue washed over the left side of their vision, and, like a lens adjusting blurs into recognizable letters, the writing focused. It said:

S DT ENABLES BRIEF TIME SPACE TRAVEL. HIGH ENOUGH DT LEVELS = TRUE TIME TRAVEL? STOPPING, STARTING, LEFT, RIGHT. EVERYTHING ENDS.

Then, underlined twice: an equation, and another line.

TWO HUMANS W HIGH DT MIN. 1 BODY?

“oh. welp.” Sans scratched the back of his head. “looks like we've found the anomaly.”

 _ **IT WOULD SEEM SO.**_ Death paused. _**WHAT WILL YOU DO NOW?**_

Sans laughed, dragging an old tarp over the determinator. “right now? i’m gonna go read papyrus his bedtime story. after that, i’m gonna hit the hay myself. tomorrow? who knows. that's the thing about free will - i can put off important decisions as long as i want.”

**Notes for the Chapter:**

> Well, that's the end of this! Thanks for reading, and I hope you enjoyed.
> 
> More Undertale fics are in the works, though I don't know which plot bunny I'm going to end up chasing. So far, I've got ideas for a Toriel-focused sequel to this, an Underswap AU, and a soulmate!AU, so if any of those sound interesting, please do keep an eye out. And if you'd like to weigh in on which of those ideas sound like things you'd read, you know where comments go!


End file.
